Curcumin inhibits epithelial-mesenchymal transition in oral cancer cells via c-Met blockade

Abstract

Oral squamous cell carcinoma (OSCC) is the most common type of oral cancer. OSCC cells are highly invasive, a characteristic that involves epithelial-mesenchymal transition (EMT); the conversion of immotile epithelial cells into motile mesenchymal cells. EMT is involved in the progression of various types of cancer by promoting tumour cell scattering and conferring to these cells cancer stem cell (CSC)-like characteristics, such as self-renewal. Hepatocyte growth factor (HGF) signalling plays an important role in EMT induction and, therefore, contributes to cell invasion and metastasis in cancer. Due to its potential chemopreventative and anti-tumour activities, curcumin has attracted much interest and has been shown to act as a potent EMT inhibitor in various types of cancer. However, at present, the potential effects of curcumin on HGF-induced EMT in OSCC have not been investigated. Here, we demonstrated that HGF signalling could induce EMT in the HSC4 and Ca9-22 OSCC cell lines via the HGF receptor c-Met and downstream activation of the pro-survival ERK pathway. Notably, curcumin inhibited HGF-induced EMT and cell motility in HSC-4 and Ca9-22 cells via c-Met blockade. Therefore, these findings establish curcumin as a candidate drug for OSCC treatment. Furthermore, curcumin was able to effectively inhibit the HGF-induced increase in the levels of vimentin by downregulating the expression of phosphorylated c-Met, an ERK. In conclusion, the results of the present study demonstrated that curcumin was able to reverse HGF-induced EMT, possibly by inhibiting c-Met expression in oral cancer cells, providing a strong basis for the development of novel approaches for the treatment of oral cancer.

Keywords: EMT; ERKs; HGF; OSCC; c-Met; curcumin.

Figure 1.

Cur inhibits HGF-induced cell invasion. Control and HGF-induced HSC-4 oral cancer cells with and without cur pre-treatment were cultured in Matrigel chambers, and the number of invading cells was scored after 48 h. (A) Representative bright-field microscopy images showing invading cells in the Matrigel chambers. Magnification, ×20. (B) Histogram showing relative cell migration (%) of invading cells after 48 h of culture, compared with HGF-induced cells. Data are presented as the mean ± SD. n=3. *P<0.05 vs. HSC-4. Cur, curcumin; HGF, hepatocyte growth factor.

Figure 2.

Cur inhibits HGF-induced cell migration. Control and HGF-induced HSC-4 oral cancer cells with and without cur pre-treatment were cultured in monolayers, and cell migration was measured by a scratch wound healing assay. (A) Representative brightfield microscopy images show wound healing at 0 and 12 h. Magnification, ×10. (B) Histogram showing relative cell migration (%), compared with control cells. Data are presented as the mean ± SD. n=3. ***P<0.001 vs. HSC-4. Cur, curcumin; HGF, hepatocyte growth factor.

Figure 3.

Cur inhibits epithelial-mesenchymal transition in HGF-induced cells. Representative western blot showing the levels of E-cadherin and vimentin in whole cell lysates from control and HGF-induced HSC4 (left) and Ca9-22 oral cancer cells (right) with and without cur pre-treatment. α-tubulin was used as a loading control. Cur, curcumin; HGF, hepatocyte growth factor.

Figure 4.

Cur inhibits c-Met phosphorylation in HGF-induced cells. Representative western blot showing the levels of c-Met and p-c-Met in whole cell lysates from control and HGF-induced HSC4 (left)and Ca9-22 oral cancer cells (right)with and without cur pre-treatment. α-tubulin was used as a loading control. Cur, curcumin; HGF, hepatocyte growth factor; p, phosphorylated.

Figure 5.

Cur-mediated c-Met blockade results in the downregulation of ERK phosphorylation. Representative western blot showing the levels of ERK and phospho-ERK in whole cell lysates from control and HGF-induced HSC4 oral cancer cells with and without cur pre-treatment. α-tubulin was used as a loading control. Cur, curcumin; HGF, hepatocyte growth factor.

Figure 6.

Cur represses the production of gelatinolytic activity. Representative gelatin zymography showing the levels of the two principal gelatinolytic activities (pro-MMP2 and pro-MMP9) in conditioned culture medium from control and HGF-induced HSC4 oral cancer cells with and without cur pre-treatment. Cur, curcumin; HGF, hepatocyte growth factor; MMP, matrix metalloproteinase.